This invention relates to a foreign matter detecting device which optically detects whether or not objects to be inspected such as beverage or medical bottles have foreign matters such as dust or leavings or cracks.
In general, returnable bottles (used beer, alcoholic, soft drink, food bottles or medical bottles) are collected to be used again. In this connection, such used returnable bottles are cleaned with a bottle cleaning device to remove the foreign matters. However, sometimes it is difficult for the bottle cleaning device to completely remove foreign matters strongly stuck to the bottle. Therefore, such bottle must be removed from the bottling line before or after the bottle cleaning process.
Although it is sufficient at low speed about 100 bottles per a minute to inspect producing bottles which are produced in a manufacturing factory, it is requested to inspect at high speed about 1,000 bottles per a minute concerning the above returnable bottles. This is based on that the transfer speed of the bottling line is higher than that of the producing line of the bottles. Further, although objects of inspection concerning the above producing bottles are cracks, bubbles and birdswings, objects of inspection concerning the returnable bottles are contaminants and foreign matters including cracks, bubbles and so on, and the scope of the objects is broader than that of the producing bottles. As described above, there are some difficult problems concerning the inspection of the returnable bottles. In addition, it is requested to detect a smaller size foreign matter or contaminant, e.g. about 0.5 mm-1.0 mm, for the returnable bottles.
By the way, two kinds of foreign matter detecting devices, one for inspecting the body (barrel) of a bottle and the other for inspecting the bottom, are known in the art. In the former device, light is externally applied to the bottle while the bottle being rotated, and light passed through the bottle is detected by a photoelectric element inserted thereinto. That is, the photoelectric element is employed to compare the quantity of transmission light obtained when a certain region of the bottle has a foreign matter to the quantity of transmission light obtained when the certain region has no foreign matter, whereby the entire body of the bottle is inspected for a foreign matter. However, the detecting device is disadvantageous in the following points: As the bottle is rotated at a high speed, the apparatus itself is liable to become bulky and mechanically complicated, and the foreign matter detecting accuracy is low and inspection speed is also very low. Furthermore, since it is necessary to insert the photoelectric element into the bottle, the air in the bottle may be contaminated, which causes a problem in food hygiene.
Further known in the art is a foreign matter detecting device in which a light source is provided on one side of a bottle to be inspected which is being rotated at high speed, to irradiate it, and a television camera using an accumulation type image pickup tube is provided on the opposite side of the bottle, to inspect the bottle. In the detecting device, the position of a bottle to be inspected is mechanically detected, and the entire bottle is inspected with one scanning line. However, the detecting device is also disadvantageous in the following points: Since the position of a bottle to be inspected is mechanically detected as described above, an error is liable to be involved in position detection, and it is difficult to uniformly inspect the surface of the bottle. Furthermore, it is impossible for one television camera to inspect two bottles or more simultaneously. Accordingly, it is difficult to increase the inspection speed. In addition, as the bottle is rotated at high speed, the device is liable to become bulky, and the mechanical handling system becomes very heavy and difficult to maintain.
In order to overcome these difficulties, a foreign matter detecting device has been proposed in the art, in which light is externally applied to a bottle which is conveyed by a conveyer and is being rotated at low speed, and a television camera provided on the opposite side of the bottle is used to inspect the entire body of the bottle. However, it is difficult to inspect bottles with high accuracy. In the end portions of the bottle, or in the portion other than the central portion of the bottle where characters or marks curved in relief are provided or the glass wall thickness is not uniform or a joint is provided, the optical path of light passed through such portions is increased or shadows are created by optical refraction, as a result of which a signal similar to that provided by a foreign matter on the bottle is produced, which makes it difficult to inspect the bottle with high accuracy.
Furthermore, a foreign matter detecting device provided with an accumulation type image pickup tube and using an electric flash as the light source is proposed in the art. However, the device still suffers from the following problems: Because of the after-image phenomenon of the image pickup tube, it is difficult to increase the inspection speed. It is necessary to frequently change the electric flash. It is still difficult to inspect with high accuracy the peripheral portions of the bottle where characters or marks curved in relief are provided and a joint is provided.